EP 0 953 372 A1 describes an apparatus for forming bellows with a filter medium folded in a zig-zag manner. The apparatus has an embossing device with two opposing embossing rollers for embossing fold lines into the filter medium and a folding device with two opposing positioning rollers. The apparatus is suitable in particular for producing bellows with variable fold heights. To this end the embossing rollers may be rotated at a variable rotational speed.
US76615408 B2 also describes an apparatus for producing bellows with a filter medium folded in a zig-zag manner, which apparatus includes an embossing device for embossing fold lines into the filter medium and a folding device, not described in greater detail. An adhesive application device for applying adhesive to the embossed filter medium is provided between the embossing device and the folding device.